I have a 2005 400 auto with 400 miles on it and it has improved the more I ride it. However, like most I feel for a 400 it was lacking alittle in power/speed so this is what I have done to my 400 so far and I couldn't be happier!!
I modified my stock muffler and drilled threw the baffles, it has a deeper tone at idle and is NOT LOUD while riding, I can't hear any difference so It will not offend anyone on the trail, My buddies stock Brute is louder than my moded cat. Next I installed a K&N filter with prefilter and a Dyno jet kit @ the current settings. 136 mainjet, 2.5 turns on mixing screw, needle e-clip on 4th notch. I spent about $100.00 for these mods and all I can say is that it was money and time well spent!! I have not had it on the trail yet but have done alittle back yard riding and it finally feels like a 400. It really get up and goes now!!

I have the clutch kit setting in my garage and will install soon and hope to upgrade tires later! I will keep ya posted about present and future mods and appreciate all your help and time!! I highly recommend what I've done on my 400 to other 400 owners! Thanks!!

I had it Dyno tested and would like to know what stock figures are compared to mine if anyone has that information.

Max power 18.66
max torque 14.22

 

Normal proceedure is to dyno first, then mod, then dyno again. Then you know what the mods were worth. I've known guys who dynoed between each mod to see what each change gained or lost.

 

Highlifter has a dyno sheet on the 400 and it looke like its just over 15 hp stock. So it looks like you gained about 3.5 hp...